1. Field
Example embodiments relate to an insulating organic polymer, an organic insulating layer formed using the insulating polymer, an organic thin film transistor comprising the insulating layer and a method of fabricating the same, and an electronic device comprising the organic thin film transistor. Other example embodiments relate to an insulating organic polymer having side chains which enable the formation of an insulating layer with a decreased surface energy to increase the degree of alignment of a semiconductor material so that the characteristics of an organic thin film transistor comprising the insulating layer are improved, an organic insulating layer formed using the insulating polymer, and an organic thin film transistor comprising the insulating layer and a method of fabricating the same, and an electronic device comprising the organic thin film transistor.
2. Description of the Related Art
Thin film transistors (TFTs) are currently used as switching devices to control the operation of respective pixels and driving devices to operate the pixels in flat panel display devices, e.g., liquid crystal display (LCD) devices and electroluminescence display (ELD) devices. Thin film transistors are also expected to be useful in plastic chips for use in smart cards and inventory tags.
Thin film transistors may include a semiconductor layer having source and drain regions, both of which are doped with higher-concentration impurities, and a channel region formed between the source and drain regions; a gate electrode insulated from the semiconductor layer and positioned in a region corresponding to the channel region; and source and drain electrodes formed in contact with the source and drain regions, respectively.
Inorganic semiconductor materials, e.g., silicon (Si), have been used as materials for channel layers of thin film transistors. However, with increasing demand for the manufacture of larger-area, flexible displays at reduced costs, organic semiconductor materials are currently used as materials for channel layers rather than inorganic semiconductor materials involving increased costs and requiring higher-temperature vacuum processes. Under these circumstances, a number of studies on organic thin film transistors (OTFTs) using an organic film as a semiconductor layer are now being undertaken.
In one example of such an organic thin film transistor, a gate insulating layer may be formed using an inorganic metal oxide, e.g., BaxSr1-xTiO3 (barium strontium titanate (BST)), Ta2O5, Y2O3 and/or TiO2, or a ferroelectric insulator, e.g., PbZrxTi1-xO3 (PZT), Bi4Ti3O12, BaMgF4, SrBi2(Ta1-xNbx)2O9, Ba(Zr1-xTix)O3 (BZT), BaTiO3, SrTiO3 or Bi4Ti3O12 by chemical vapor deposition, physical vapor deposition, sputtering and/or sol-gel coating. This organic thin film transistor has been reported to have reduced driving voltage and threshold voltage because it utilizes a high-k dielectric constant (κ) insulating film.
Although the driving voltage of the OTFT may be reduced to some degree, other characteristics (e.g., charge carrier mobility) of the OTFT are still unsatisfactory. Furthermore, because most fabrication processes require an increased temperature of about 200° C. to about 400° C., plastic substrates suitable for use in the manufacture of flexible displays may not be used and common wet processes, e.g., simpler coating and printing, may not be applied to fabricate the devices.
The surface characteristics of an insulating layer in an organic thin film transistor play a critical role in improving the performance of the organic thin film transistor. Thus, a great deal of research has been conducted to increase the charge carrier mobility at the interface between a gate insulating layer and an organic semiconductor layer in an organic thin film transistor and to form a gate insulating layer by simple processes. A decreased surface energy of an insulating layer (e.g. a highly hydrophobic insulating layer) in an organic thin film transistor leads to an increase in the degree of alignment of a semiconductor material constituting an organic semiconductor layer, thus achieving improved performance of the transistor. Some methods have been attempted to increase the mobility of organic thin film transistors by surface treatment of insulating layers. However, the additional surface treatment results in undesirable processability of the insulating layers and incurs considerable processing costs.